Re^2: How to evaluate a mathematical formula that is stored in another file?

Thanks your code greatly helped me to get part of my results. But can you explain these two lines below? Thanks.

    while ($formula =~ s|([a-z]+)|$data{$1}//' '|e) {
        push @error, $1 unless exists $data{$1};
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Re^3: How to evaluate a mathematical formula that is stored in another file? by hdb (Monsignor) on Mar 22, 2018 at 11:39 UTC
In my simplistic example code I assumed that a variable name consists of lower case letters. The regular expression `([a-z]+)` finds any consecutive sequence of (at least one) lower case letters. It is then replaced by `$data{$1}//' '` where `$1` stands for the found sequence. `$data{$1}` is the value assigned to that sequence ie the variable name. If it does not exist in the hash `%data` the expression `//' '` ensures that a blank is used instead (also makes sure that no warning is issued). I have used `s\|\|\|` instead of the more common `s///` to avoid confusion on the `//` operator. In the `push` statement I store the found sequence as in `$1` in the array `@error` if `%data` did not contain a value for the variable. This is some kind of crude error handling and I can list the names of variables without values further below in the code. Again, this is only a simplistic example, and not the only way to look at your requirements. The evil `eval` is still not fully defused and one could create havoc with mischievous inputs in the values or formulae provided.	[reply] [d/l] [select]
Re^4: How to evaluate a mathematical formula that is stored in another file? by skooma (Novice) on Mar 29, 2018 at 05:48 UTC
Thanks.	[reply]